Throughout most of George Washington’s life he had problems of continuing deterioration of his teeth. This caused him a lot of pain, and none of the dentists he went to knew what to do besides take them out. Slowly but surely all of Washington’s teeth were extracted. In 1772 Dr. Baker of Philadelphia extracted several. Finally, George had to have false teeth made. They were made out of hippopotamus ivory and cow’s tooth, carved by hand, and held in his mouth with metal springs. These false teeth were a little large for his mouth, creating a peculiar expression, which is exhibited in many of his portraits. Today, the teeth can be viewed at the University of Maryland’s National Museum of Dentistry.

This letter, written in 1781, requests cleaning utensils for his false teeth. Having been captured by the British before it reached its destination, the letter may have led the British forces to understand the where-abouts and movements of the General. However, this is not confirmed.

The uncanny valley hypothesis holds that when robots and other facsimiles of humans look and act almost like actual humans, it causes a response of revulsion among human observers. The “valley” in question is a dip in a proposed graph of the positivity of human reaction as a function of a robot’s lifelikeness.
It was introduced by Japanese roboticist Masahiro Mori as “Bukimi no Tani Genshō” in 1970, and has been linked to Ernst Jentsch’s concept of “the uncanny” identified in a 1906 essay, “On the Psychology of the Uncanny”. Jentsch’s conception is famously elaborated upon by Sigmund Freud in a 1919 essay titled “The Uncanny” (“Das Unheimliche”).
Hypothesis
Mori’s hypothesis states that as a robot is made more humanlike in its appearance and motion, the emotional response from a human being to the robot will become increasingly positive and empathic, until a point is reached beyond which the response quickly becomes that of strong repulsion. However, as the appearance and motion continue to become less distinguishable from a human being, the emotional response becomes positive once more and approaches human-to-human empathy levels.
This area of repulsive response aroused by a robot with appearance and motion between a “barely human” and “fully human” entity is called the uncanny valley. The name captures the idea that a robot which is “almost human” will seem overly “strange” to a human being and thus will fail to evoke the empathic response required for productive human-robot interaction.
Theoretical basis
Hypothesized emotional response of human subjects is plotted against anthropomorphism of a robot, following Mori’s statements. The uncanny valley is the region of negative emotional response towards robots that seem “almost human”. Movement amplifies the emotional response. A number of theories have been proposed to explain the cognitive mechanism underlying the phenomenon:
Mate selection. Automatic, stimulus-driven appraisals of uncanny stimuli elicit aversion by activating an evolved cognitive mechanism for the avoidance of selecting mates with low fertility, poor hormonal health, or ineffective immune systems based on visible features of the face and body that are predictive of those traits.
Mortality salience. An “uncanny robot elicits an innate fear of death and culturally-supported defenses for coping with death’s inevitability…. [P]artially disassembled androids… play on subconscious fears of reduction, replacement, and annihilation: (1) A mechanism with a human facade and a mechanical interior plays on our subconscious fear that we are all just soulless machines. (2) Androids in various states of mutilation, decapitation, or disassembly are reminiscent of a battlefield after a conflict and, as such, serve as a reminder of our mortality. (3) Since most androids are copies of actual people, they are Doppelgaenger and may elicit a fear of being replaced, on the job, in a relationship, and so on. (4) The jerkiness of an android’s movements could be unsettling because it elicits a fear of losing bodily control.”
Pathogen avoidance. Uncanny stimuli may activate a cognitive mechanism that originally evolved to motivate the avoidance of potential sources of pathogens by eliciting a disgust response. “The more human an organism looks, the stronger the aversion to its defects, because (1) defects indicate disease, (2) more human-looking organisms are more closely related to human beings genetically, and (3) the probability of contracting disease-causing bacteria, viruses, and other parasites increases with genetic similarity.” Thus, the visual anomalies of android robots and animated human characters have the same effect as those of corpses and visibly diseased individuals: the elicitation of alarm and revulsion.
Sorites paradoxes. Stimuli with human and nonhuman traits undermine our sense of human identity by linking qualitatively different categories, human and nonhuman, by a quantitative metric, degree of human likeness.
Violation of human norms. The uncanny valley may “be symptomatic of entities that elicit a model of a human other but do not measure up to it.” If an entity looks sufficiently nonhuman, its human characteristics will be noticeable, generating empathy. However, if the entity looks almost human, it will elicit our model of a human other and its detailed normative expectations. The nonhuman characteristics will be noticeable, giving the human viewer a sense of strangeness. In other words, a robot stuck inside the uncanny valley is no longer being judged by the standards of a robot doing a passable job at pretending to be human, but is instead being judged by the standards of a human doing a terrible job at acting like a normal person.
Western constructions of human identity. The existence of artificial but humanlike entities is a threat to human identity as socially constructed in the West and the Middle East but not in the Far East, partly because Western philosophy and religions (e.g., Judaism, Christianity, and Islam) emphasize human uniqueness as compared to Eastern philosophies and religions (e.g., Buddhism, neo-Confucianism, Taoism, Shinto, Japanese adaptation of biological materialism). An example can be found in the theoretical framework of the western psychologist Irvin Yalom. Yalom explains that humans construct psychological defenses in order to avoid existential anxiety stemming from death. One of these defenses is “specialness”, the irrational belief that aging and death as central premises of life apply to all others but oneself. The experience of the very humanlike “living” robot can be so rich and compelling that it challenges humans’ notions of “specialness” and existential defenses, eliciting existential anxiety.
Design principles
A number of design principles have been proposed for avoiding the uncanny valley:
Design elements should match in human realism. For a robot to give a more positive impression, its degree of human realism in appearance should match its degree of human realism in behavior. If an animated character looks more human than its movement, this gives a negative impression. A robot may look uncanny when human and nonhuman elements are mixed.
Appearance and behavior should match ability. In terms of performance, if a robot looks too appliance-like, people will expect little from it; if it looks too human, people will expect too much from it.
Human facial proportions and photorealistic texture should only be used together. A photorealistic human texture demands human facial proportions, or the computer generated character can fall into the uncanny valley. Abnormal facial proportions, including those typically used by artists to enhance attractiveness (e.g., larger eyes), can look eerie with a photorealistic human texture. Avoiding a photorealistic texture can permit more leeway.
Criticism
A number of criticisms have been raised concerning whether the uncanny valley exists as a unified phenomenon amenable to scientific scrutiny:
Good design can lift human-looking entities out of the valley. David Hanson has criticized Mori’s hypothesis that entities approaching human appearance will necessarily be evaluated negatively. He has shown that the uncanny valley that Karl MacDorman and Hiroshi Ishiguro generated – by having participants rate photographs that morphed from humanoid robots to android robots to human beings – could be flattened out by adding neotenous, cartoonish features to the entities that had formerly fallen into the valley.
The uncanny appears at any degree of human likeness. Hanson has also pointed out that uncanny entities may appear anywhere in a spectrum ranging from the abstract (e.g., MIT’s robot Lazlo) to the perfectly human (e.g., cosmetically atypical people). Capgras syndrome is a relatively rare condition in which the sufferer believes that people (or, in some cases, things) have been replaced with duplicates. These duplicates are rationally accepted to be identical in physical properties, but the irrational belief is held that the “true” entity has been replaced with something else. Some sufferers of Capgras syndrome claim that the duplicate is a robot. Ellis and Lewis argue that the syndrome arises from an intact system for overt recognition coupled with a damaged system for covert recognition, which leads to conflict over an individual being identifiable but not familiar in any emotional sense. This supports the view that the uncanny valley could arise due to issues of categorical perception that are particular to the manner in which the social brain processes information.
The uncanny valley is a heterogeneous group of phenomena. Phenomena labeled as being in the uncanny valley can be diverse, involve different sense modalities, and have multiple, possibly overlapping causes, which can range from evolved or learned circuits for early face perception to culturally-shared psychological constructs. People’s cultural backgrounds may have a considerable influence on how androids are perceived with respect to the uncanny valley.
Transhumanism
According to writer Jamais Cascio, a similar “uncanny valley” effect could show up when humans begin modifying themselves with transhuman enhancements (cf. body modification), which aim to improve the abilities of the human body beyond what would normally be possible, be it eyesight, muscle strength, or cognition. So long as these enhancements remain within a perceived norm of human behavior, a negative reaction is unlikely, but once individuals supplant normal human variety, revulsion can be expected. However, according to this theory, once such technologies gain further distance from human norms, “transhuman” individuals would cease to be judged on human levels and instead be regarded as separate entities altogether (this point is what has been dubbed “posthuman”), and it is here that acceptance would rise once again out of the uncanny valley. Another example comes from “pageant retouching” photos, especially of children, which some find disturbingly doll-like.